With few exceptions, Machine Shops each serve a local market rather than catering to a national (let alone an international) customer base. In turn, most of them concentrate on jobs that can be considered in terms of general rather than specialized machining. In other words, they produce parts by turning, milling, boring, and grinding metal, but they don't often go beyond these processes.
Additional note: Tool and Die Shops differ from Machine Shops and have a category of their own. Their emphasis is on producing tooling, patterns, dies, fixtures, gages, and parts that involve one form or another of special or sophisticated machining. As with Grinding companies and their like, their numbers aren't too unmanageable, and there is no benefit in breaking them up into location subcategories.